This application claims benefit under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 60/227,675, filed Aug. 24, 2000.
The present invention relates to nucleic acid (e.g., DNA or RNA) sampling. More particularly, this invention relates to transdermal nucleic acid sampling. The present invention uses skin-piercing microprojections to pierce skin cells and affect transdermal nucleic acid sampling.
DNA testing is presently performed by blood sampling or tissue swabbing followed by polymerase chain reaction (PCR) amplification of the DNA and then analysis of the amplified DNA. Blood sampling using a syringe is invasive and painful. Tissue swabbing is inconvenient and uncomfortable for many patients. One common procedure for sampling DNA uses buccal mucosal tissue samples obtained by rotating cyto brushes vigorously along the inside of the cheek for about 30 seconds.
There have been many attempts to enhance transdermal flux by mechanically puncturing the skin prior to transdermal drug delivery. See for example U.S. Pat. Nos. 5,279,544 issued to Gross et al., 5,250,023 issued to Lee et al., and 3,964,482 issued to Gerstel et al. These devices utilize solid and hollow microprojections to pierce the outer layer of the skin.
There have also been attempts to sample body analytes (e.g., glucose) contained in interstitial fluid using devices having similar skin-piercing microprojections. The analyte content in the interstitial fluid is then correlated with that in the blood. See for example, Cormier et al WO 97/48441; Joseph, U.S. Pat. No. 5,161,532; Erickson et al., U.S. Pat. No. 5,582,184; Brinda, U.S. Pat. No. 5,682,233; Erickson et al., U.S. Pat. No. 5,746,217 and Erickson et al., U.S. Pat. No. 5,820,570. Daddona et al. U.S. Pat. No. 6,091,975 provides a diagnostic device having stratum corneum-piercing microprojections. Electrochemical sensors are placed directly on the microprojections for sensing/measuring body analyte concentrations such as blood glucose concentration. One of the advantages of sampling interstitial fluid is that the wound created in the skin is not as deep as the wound needed for blood sampling. Thus, interstitial fluid sampling using such stratum corneum piercing microprojections is generally considered less invasive than blood sampling.
However, there is still a need for less invasive sampling of nucleic acids for the purposes of genetic testing (e.g., paternity testing, matching blood/semen samples to individuals in police/criminal detective work), medical diagnostics (e.g., screening patients for the presence of a disease and/or for predisposition towards disease such as heart disease), and the like.
The present invention provides a method for transdermal DNA sampling using a reproducible, high volume production, low-cost device. The invention comprises piercing through the outermost layer (i.e., the stratum corneum layer) of the skin and into the underlying epidermis layer, or into both the epidermis and dermis layers, with a plurality of microprojections. Individual skin cells within the epidermis/dermis layers are pierced, causing the cellular contents, including the cells"" nucleus and its nucleic acids, to be released. The nucleic acids are coated onto the surfaces of the microprojections and/or absorbed into an absorbant coating on the microprojections. The microprojections typically have a length of less than about 0.4 mm and a width and thickness which is even smaller.
The method of the present invention can also be used to extract and sample nucleic acids released into the skin""s interstitial fluid. As before, the outermost stratum corneum layer of the skin is pierced to form pathways through which the interstitial fluid, containing the nucleic acids, is withdrawn (i.e., sampled). Optionally, the sampling device used with this embodiment of the present invention can apply a partial vacuum (also referred to herein as xe2x80x9cnegative pressurexe2x80x9d) to the microcut skin. The negative pressure causes interstitial fluid to efflux from the microcuts. The interstitial fluid is collected, the nucleic acids contained therein is amplified using standard polymerase chain reaction (PCR) techniques, and then the amplified nucleic acids are analyzed.
In one aspect of the invention, the device for piercing the skin comprises a sheet having a plurality of openings therethrough, and a plurality of microprojections integral therewith and extending downward (i.e., in a direction toward the skin) therefrom. The optional negative pressure driven device applies a partial vacuum (i.e., suction) to the microcuts through the openings in the sheet.